Artemia Production for Marine Larval Fish Culture

The brine shrimp (Artemia) is in
the phylum Arthropoda, class
Crustacea. Artemia are zooplankton,
like copepods and Daphnia,
which are used as live food in the
aquarium trade and for marine
finfish and crustacean larval culture.
There are more than 50 geographical
strains of Artemia. Many
commercial harvesters and distributors
sell brands of various
qualities. Approximately 90 percent
of the world's commercial
harvest of brine shrimp cysts (the
dormant stage) comes from the
Great Salt Lake in Utah. However,
the lake's cyst production is heavily
influenced by freshwater
inflow, and the supply varies dramatically.
The cost of good quality
cysts fluctuates with supply and
demand; buyers might expect to
pay $12 to $40 or more per pound
(1/2 kg). Normally 200,000 to
300,000 nauplii might hatch from
each gram of high quality cysts.
This publication describes the
process of hatching Artemia cysts
for use as larval food for cultured
species, and the benefits of
Artemia as a food source.

Background

Artemia are extremely euryhaline,
withstanding salinities from 3 ppt
to 300 ppt. They can even survive
short periods of time in freshwater,
but cannot reproduce in it.
Artemia survive temperatures
ranging from 15 to 55 oC (59 to
131 oF). They have two modes of
reproduction. Sometimes nauplii
(first Artemia swimming stage)
hatch in the ovisac of the mother
and are born live. However, when
the body of water where adult
Artemia are living begins to dry
up and salinities rise, embryos are
encased in a hard capsule, or cyst,
so that they are protected and can
hatch later when conditions are
better. The cyst is 200 to 300
micrometers in diameter, depending
upon the strain. Its external
layer is a hard, dark brown shell.
Dry conditions cause the encysted
embryo to enter a dormant state,
which allows it to withstand complete
drying, temperatures over
100 oC (212 oF) or near absolute
zero, high energy radiation, and a
variety of organic solvents. The
dehydrated cyst can be stored for
months or years without loss of
hatchability. Only water and oxygen
are required to initiate the
normal development of the
Artemia embryo, but it does help
the hatch rate to maintain the
temperature above 25 oC (77 oF)
and place a light near the eggs.
The durable, easily hatched cyst
makes Artemia a convenient, constantly
accessible source of live
feed for the finfish hatchery operator.
Artemia cysts are best stored
in a tightly sealed container in a
cool, dry environment and, if possible,
vacuum packed.

Within 15 to 20 hours after being
placed in seawater at 28 oC (82
oF), the shell breaks and the prenauplius
in E-1 stage appears
(Fig. 1a). For the first few hours,
the embryo hangs beneath the
cyst shell in what is called the
umbrella stage. The newly
hatched Artemia relies on its yolk
sac for nutrients because its
mouth and anus are not fully
developed. The pre-nauplius E-2
stage (Fig. 1b) is then released as a
free-swimming nauplius (Fig. 1c)
called an Instar 1 nauplius. In this
stage it is brownish orange because
of its yolk reserves. It uses
specially modified antennae for
locomotion and later for food filtering.
Approximately 12 hours
after hatch it molts into the second
larval stage (Instar II) and starts
filter feeding on microalgae, bacteria
and detritus. The Artemia nauplius
can live on yolk and stored
re-serves for up to 5 days or
through the Instar V stage (Fig.
1d), but its caloric and protein
content diminish during this time. The nauplius progresses through
15 molts before reaching adulthood
in approximately 8 days.

The goal of the hatchery manager
is to use the Artemia as feed as
soon as possible after they hatch
because that is when they are
most nutritious. However, the
lipid level and fatty acid composition
of newly hatched Artemia
nauplii can be highly variable,
depending upon the strain and
year class. Many researchers have
studied the levels of highly unsaturated
fatty acids (HUFA) in
Artemia. Most of these studies indicate that the performance of
larval fish is directly related to the
level of HUFA in Artemia being
fed and that essential fatty acids
are the principal food value of
Artemia. When Artemia contain
low levels of HUFA, the survival
of larval fish declines.

It is important to feed Artemia
nauplii to fish larvae as soon as
possible after hatching to take full
advantage of the yolk and stored
reserves found in freshly hatched
Instar I nauplii (Fig. 1c). If there is
a delay in feeding Artemia, they
may also become too fast and too
large for the fish larvae to catch
and eat. Also, freshly hatched
nauplii are dark orange and much
easier to see than older nauplii,
which are transparent. Some
strains of Artemia may be too large
for the fish being cultured, so it
would be wise to ask other hatchery
managers for their suggestions
about which strains to use.
Figure 2 shows the size of a freshly
hatched Artemia nauplius relative
to a 12- to 13-day post-hatch
red drum larva. Feeding an oversized
Artemia strain can cause fish
larvae to grow poorly or even
starve.

Optimum conditions for hatching Artemia cysts

The optimal conditions for hatching
Artemia are: 1) temperature
above 25 oC (77 oF), with 28 oC
(82 oF) being optimum; 2) salinity
of 5 ppt (1.030 density); 3) heavy,
continuous aeration; 4) constant
illumination (example: two 40-
watt fluorescent bulbs for a series
of four 1-liter hatching cones); and
5) a pH of about 8. Stocking density
is set by adding no more than
5 grams of cysts per liter of water.
Good circulation is needed to
keep the cysts in suspension. A
container that is V-shaped or
cone-shaped is best (2-liter bottles
work well; glue a valve on the
bottle cap and invert it). The best
container is a separation column,
found in any lab supply, although
it is more expensive. Unhatched
cysts, empty shells and hatched
nauplii can be easily removed
separately. The hatching percentage
and density are usually a
function of water quality, circulation,
and the origin of the cysts.

Preparation and use of Artemia

There are seven tasks involved in feeding Artemia to larvae.

Determine the weight of Artemia cysts required to feed the larvae in a tank of known volume.

Hydrate and decapsulate cysts (decapsulation is optional, but recommended).

Incubate cysts.

Separate cysts from shells and debris (not necessary if cysts were decapsulated).

Count the hatched Artemia.

Calculate the number of Artemia remaining in the rearing tank from the previous feeding.

Calculate the number of Artemia nauplii required by the larvae and transfer them to the rearing tank.

Be careful with step number 6, as remaining nauplii may have little nutritional value and may need to be flushed out of the system.

Details of each of the tasks will be
discussed in the following smallscale
example. Materials and
equipment needed are:

Artemia cysts

two 250-ml (8.5-fluid ounce)
beakers

distilled water

household bleach

sodium hydroxide (NaOH)

1-liter Imhoff cone or settling
column

low-pressure air supply (aquarium
pump)

seawater or equivalent (salinity
of 5 to 32 ppt)

siphon tube (approximately 4
feet long) or a valve at the bottom of the cone

1-ml pipet

10-ml pipet

1. Determine the amount of
Artemia cysts required

Artemia nauplii are maintained in
the larval culture tank at densities
of 0.5 to 2 per ml for most species
of finfish and up to 6 per ml in the
more advanced larval shrimp
stages. To estimate the amount of
Artemia required one must consider
both the volume of the tank
and the expected number of
Artemia the larvae will consume.
Based on the stage or the age of
the larvae, estimate a daily
Artemia requirement per ml. This
feeding rate can be adjusted
slightly, depending on the stocking
density (number of target larvae
per liter) and the rate at which
the Artemia are consumed. The
total requirement is then calculated
by multiplying the predicted
requirement per ml by the total
volume of the rearing tanks. Each
gram of cysts contains approximately
200,000 to 300,000 cysts.
Artemia generally have at least a
50 percent hatch. Experience with
your specific brand will allow you
to adjust these figures.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 97-38500-4124 from
the United States Department of Agriculture, Cooperative States Research, Education, and Extension Service.